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Why is the Su-27 so much larger than the MiG-29?
I was watching the following video of the Russian Knights and Swifts aerobatic teams flying together in formation. The contrast in the size of their airplanes is striking.

Why was the Su-27 designed to be so much larger than the MiG-29?
Do the two planes have very different missions?

The Su-27 and Mig-29 were the result of high-low concept subscribed by both the USAF and Soviet Air Force (VVS) in the 1970s. Basically, this involved the development of two different fighters, a high performance medium weight fighter crammed with every advanced technology (which made it expensive) and a low cost light weight fighter to make up the numbers.
In this direction, the USAF announced the FX (Fighter eXperimental) program, which resulted in the McDonnell Douglas F-15 Eagle (designed to counter the misunderstood Mig-25), followed by the LWF (Light Weight Fighter) competition, that gave birth to the General Dynamics F-16 Fighting Falcon.
The Soviet equivalent of these programs was the PFI( Perspektivnyi Frontovoy Istrebitel, Perspective Frontline Fighter), which called for a high performance multirole aircraft to counter the new generation US aircraft and the LFI (Lyogkiy Frontovoy Istrebitel, Light Frontline Fighter), which called for a low cost fighter with respectable ground attack capabilities.
The PFI was required to operate 250-300 km beyond the frontline, with sizeable internal fuel and a comprehensive Communications, navigation, avionics and weapons suite. The LFI, on the other hand was required to operate 100-150 km beyound the frontline, while being easy (read cheap) to build and maintain and capable of using semi-prepared strips while carrying limited armament (initially limited to a couple of medium range AAMs and gun).
In 1972, the VVS tasked the Sukhoi bureau to build the PFI, resulting in the Sukhoi Su-27, while the Mikoyan bureau got the LFI, resulting in Mikoyan MiG-29.

F-15 and F-16; image from sunketh.wordpress.com
Basically, Su-27 is to Mig-29 what F-15 is to F-16; hence the size difference.

This is an interesting perspective, comparing the US and the Soviet solution to basically the same problem. Your answer highlights the different approaches taken by the Americans and the Soviets. While the US developed two very different planes, the Soviets more or less went for a scaled solution, since the MiG 29 and the Su 27 share their aerodynamic layout.

The Su-27 was design to fly escort for long distance bombers, whereas, the Mig-29 was designed for front line action. This distinction in the primary mission of the two aircrafts becomes apparent when you look e.g. at the range.
More fuel means more weight, means more powerful engines, means more fuel, etc.


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How to handle the formula for computing net thrust of closely coupled engine systems for an engine with a nacelle that has non-circular dimensions?
I am working on a paper and I wish to use this equation for calculating the thrust of an engine in a nacelle:
$$ Fn= \displaystyle \oint V_x\rho\vec V\cdot\vec n \ dA + \displaystyle \oint(P-P_{\infty})\vec n_x \ dA - \displaystyle \oint \vec \tau_x \ dA$$
This equation was given for a simplified case: the common circular nacelle. However, I would like to apply it to the flattened bottom nacelle as on the 737.

I have attempted to fit an equation to this by adjusting the parameters of a cardiod in polar coordinates. I'm having some trouble changing the above to polar integrals, however I'm not sure as to how this conversion would affect the rest of the equation. I could apply the rectangular form instead and keep the above integrals, but I don't think there is a away to express y explicitly in terms of x; it must be done implicitly and so that integral wouldn't really be possible.

Can we get some @PeterKampf love on this question?

Did you mean to include an image under "here:"

No, that was an error on my part, thanks for pointing that out. Unless you think I should place an image there for help.

I really don't see any aspect of the formula that limits it being applied to only a circular exhaust nozzle. But it all seems a very pointless formula anyway, because to apply it you need to know the pressure and velocity in a piecewise fashion, across the whole face of the nozzle exit plane. Engine performance programs don't give you that data. You would need a 3D CFD model of the nozzle exit. And after all that effort, are you really going to end up with a more accurate answer than the standard 1D thrust equation: FN  = m  x  (Ve - Vi) + A8 x (Ps8 - Pamb) ?

... You raise a valid point @Penguin. I will take a further look at this from your point of view, but for the time being, if you'd like to just post this as an answer I will mark it as accepted if I don't get anything more detailed by today. Thanks for your second perspective.

Hi @Jihyun.  Glad my comment helped. I'll probably leave it as a comment, as it isn't a very comprehensive answer, and I am not really motivated by points. Maybe someone will give a more complete answer. I am curious where the last term in your equation comes from - the other terms are recognisable as the two terms in the 1D equation, but the last one I don't know where that comes from. Cheers.

Great, thanks still for the clarification @Penguin. I'll take a look at that last term.

In review of my earlier question, @Penguin and my math professor's commentaries agree on the point that the equation $$ Fn= \displaystyle \oint V_x\rho\vec V\cdot\vec n \ dA + \displaystyle \oint(P-P_{\infty})\vec n_x \ dA$$ is the meat of the problem and that when you get the piecewise pressure and velocity, the third term $$- \displaystyle \oint \vec \tau_x \ dA$$ was inconsequential, as it (as far as I can mathematically deduce) describes the core cowl and the external nacelle. As it is an independent characteristic, I'm confident I can just adjust the modelling for a different shape. Thanks again to @Pengiun for providing an outside perspective to my dilemma.

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What is the difference between MIL-H-5606 and MIL-PRF-5606 hydraulic fluid?
what is the meaning of PRF here and can you differentiate them visually ?

About 25 years ago, there was a major effort to revise MIL standards and specifications.  The biggest change in MIL specs was to move away from a design or manufacture spec to a performance spec. The downside of the old specs were that they didn't allow for an improved product without getting the spec revised.  By switching to performance spec (what it must do as opposed to how to make it), improvements can be made without spec revisions and contract revisions (that call out the specs) ultimately saving everyone time and money while delivering products that use up to date technology.
In your case, MIL-H-5606 is the 'old' spec.  The H is taken from the primary application, in this case "Hydraulics".  The current spec is MIL-PRF-5606.  PRF is used to indicate a 'performance' specification.
'MIL-PRF' and other abbreviations are defined within DoD 4120.24-M, [2], Defense Standardization Program (DSP) Policies and Procedures, March 2000, OUSD (Acquisition, Technology and Logistics).

True, though approved parts lists/approved vendor lists make the distinction somewhat moot.

MIL-H-5606 and MIL-PRF-5606 are US specifications for hydraulic fluid based on mineral oil. They are used in US military 3000 PSI hydraulic systems.
The biggest draw back is their flammability, which is why their use in new commercial aircraft designs has been eliminated. However, many piston general aviation aircraft still depend on -5606 hydraulic fluid.
MIL-H-5606 is obsolete and superseded by MIL-PRF-5606.

Depends on you definition of 'commercial'. Small aircraft like Cessnas and Pipers use 5606 for brakes, gear, and some autopilots. Some of those are in commercial service.

Many business jets also use MIL-H-5606 for their hydraulic systems.

Cessna, Bananza, and Navion use MIL-H-5606 for their hydraulic systems.

Commonly MIL-H-5606 is replaced with the compatible MIL-H-83282 or now PRF due to its increased flammability resistance.  As long as the operating temp range stays above -40.  It also is not restricted to piston engine aircraft, Beechcraft King Air with a PT-6 as well as many turbine commercial helicopters use one or both of these fluids. Sikorsky, Bell and Airbus helicopters to name a few.

PRF is from the MIL-PRF portion of the Performance Specification and is not specific to this item number. See MIL-PRF.
From AeroShell handbook on hydraulic fluids...

Although the military did not move to phosphate ester type fluids they did identify the need for a more fire resistant fluid as a direct replacement for MIL-H-5606. As a result a synthetic hydrocarbon-based fluid, MIL-H-83282 was developed. This fluid is completely compatible with MIL-H-5606 fluids and MIL-H-5606 hydraulic system materials. All physical properties of MIL-H-83282 (now MIL-PRF-83282) were equivalent to or superior to those of MIL-H-5606 (now MIL-PRF-5606) except for low temperature viscosity. In particular all fire resistant properties of MIL-PRF-83282 are superior to those of MIL-PRF-5606. More recently MIL-PRF-87257 was introduced in order to address the concerns over the low temperature viscosity of MIL-PRF-83282.

Visually, there is no distinctive difference between the old 5606 and the replacement variants of 83282.
My take is that we should all be moving to 83282.  Another part number to remember...

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Why does the B-2 have a smaller payload than other bombers of comparable size?
B-2 Spirit1
Payload
40,000 pounds (18,144 kilograms)
Wingspan
172 feet (52.12 meters)
Weight
160,000 pounds (72,575 kilograms)
Maximum takeoff weight
336,500 pounds (152,634 kilograms)
Range
approximately 6,000 nautical miles (9,600 kilometers)
B-52 Stratofortress2
Payload
70,000 pounds (31,500 kilograms)
Wingspan
185 feet (56.4 meters)
Weight
Approximately 185,000 pounds (83,250 kilograms)
Maximum takeoff weight
488,000 pounds (219,600 kilograms)
Range
8,800 miles (7,652 nautical miles)
B-1B Lancer3,4
Payload
75,000 pounds (34,019 kilograms)
Wingspan
137 feet (41.8 meters) extended forward, 79 feet (24.1 meters) swept aft
Weight
approximately 190,000 pounds (86,183 kilograms)
Maximum Takeoff Weight
477,000 pounds (216,634 kilograms)
Range
5,100 nmi (5,900 mi; 9,400 km)

The US Air Force web-site says:

The revolutionary blending of low-observable technologies with high aerodynamic efficiency and large payload gives the B-2 important advantages over existing bombers.

But in comparison with the other bombers, including much older B-52, it appears to be less aerodynamically efficient and carries less payload.
Why does the B-2 carry a much smaller payload than the other bombers of comparable size? Does it signify, that B-2 has worse aerodynamic characteristics? If yes - what are causes of it?

@Federico rant on then! ;)

@FreeMan- leaving aside general answer issues, HNQ frequently leads to  poor   answers being upvoted

Seems like a good question.

I think it's good, albeit badly researched question.

The simple answer is that it is optimized for being low observable/stealthy, and long range, rather than for maximum payload.
When you design an aircraft, you make a variety of trade offs depending upon which features are most important for that design.  The design of the B-2, which reaches back into the 1980's1, put a premium on the ability to avoid being detected by radar.  This informed the shape.  The USAF's strategic purpose for that aircraft was to enable it to reach globally, so that it could be launched form the continental US or a forward deployed base.  This put a premium on range/fuel capacity.
@Durandal points to another detail/difference: The B52 and B1 both can carry ordnance on external hard points (and this is a must to get up to the cited payloads). The B2 has no such hard points because it would nullify its stealth capability. There is simply no room to put more munitions within the bomb bay.
With the advent of precision weapons, which were in parallel development to the B-2, the raw tonnage wasn't as important as getting to the target area, and getting out "without being seen."
Because aircraft are all constrained somewhat by the cube/square law in terms of size, the trade offs/compromises on that model arrived at a payload that fit in with the rest of the requirements.
Both the B-52 and B-1 were build under a different design paradigm, under different requirements combinations, and were "pre-stealth" bombers: the B-52 was meant to get the most range and raw payload together, while the B-1 combined speed (supersonic, back when speed was perceived to be at a premium) and payload foremost.  While both have since benefitted from the use of precision munitions, the original designs (all nuclear weapons carriage considered) had to account for the problem of non-precision munitions shortcomings with accuracy.  (Experiences in WW II informed this problem, as did experience in Viet Nam).  You need to drop a pattern of "x many bombs" to have a high probability of hitting a given target.

1 Insofar as the "flying wing" idea for the shape of the B-2, the initial attempts in that direction go back to the 1930's and the Ho_229 as so @paracetamol kindly reminds us.  Also, and FWIW, it is related to a DARPA  project that goes back to the 1970's (stealth / radar resistant in general) that was compromised publicly by President Carter during a press conference.  Actually, those paying attention had heard of it from Kelly Johnson: In fact, that existence was far from secret. On July 23, 1976, readers of Aerospace Daily were informed that Clarence L. (Kelly) Johnson, "the nation's premier aircraft designer" and architect of the U-2 and SR-71 spy planes, was bulding "a new 12,000-pound, one-man Stealth aircraft" at the Lockheed plant in Burbank, Calif. The magazine claimed that the $90 million program, sponsored by the Defense Advanced Research Projects Agency, was designed "to reduce aircraft visibility -- optical, acoustic, and radar signatures -- through new technology."

"The design of the B-2, which reaches back into the 80's, put a premium on the ability to avoid being detected by radar." That "design" however, was developed as far back as the 30's [https://en.wikipedia.org/wiki/Horten_Ho_229] ;)

@paracetamol while that hasn't as much to do with the final B-2 stealth, range, and payload decisions, "Flying wing" as a concept ... good point. I'll add that. :-)

There is a missed aspect. The B52 and B1 both can carry ordonance on external hardpoints (and this is a must to get up to the cited payloads). The B2 has no such hardpoints because it would nullify its stealth capability. The plane itself could most likely carry larger payloads, but there is simply no room to put more munitions within the bomb bay. Both B1 and B52 have been upgraded to carry an assortment of contemporary guided munitions (or in case of the B1 cruise missiles were among its initial capability already).

@Durandal Fair point, and F-35 is running into similar challenges though I recall that it has provision for external stores.  I paraphrased your point, and credit to you.  Thank you.

Look at B-2 max. takeoff weight. It is much smaller then of the other bombers.

@GillBates And your point is? I refer you to the cube/square law yet again.  Aircraft design takes a great many things into account.  Suggest you do some research and find out if you can what the minimum acceptable pay load was for the requirement to which the design was adapted.  Since you have chosen to believe that a single metric, payload, is somehow the driver to this design, I am not sure what further help any of us can be for you.

@KorvinStarmast, 1 - This is a bomber, so it's reasonable to assume, that payload size matter for it. 2 - The USAF and Northrop Grumman pages states, that payload is the key advantage of the aircraft. 3 - The USAF page also says, that aerodynamic efficiency is the key advantage of B-2.

@GillBates You are mixing apples and oranges; it's payload size is informed by the aerodynamic properties of the flying wing and range; your juxtaposition with B-1 and B-2 is in a lot of ways a non sequitur. Not built with identical mission requirements.  (And sadly, they curtailed the buy thanks to the Clinton era austerity.  The production run was supposed to be quite a bit larger originally)

The B-1 and B-52 were introduced at a time when most bombs were not guided. Thus, the mission for these older bombers required larger payloads to deliver large quantities of "dumb" bombs to blanket the target area. The B-2 was introduced in 1997, at a time when guided smart bombs were being used more frequently. The B-2 carries fewer, but much more accurate (guided) weapon systems.

For several reasons:

Philosophy of Use: the B-2 was designed from the drawing board upward to be a nuclear bomber to specifically used for penetration of dense Integrated Air Defense Systems (IADS) to strike specific high value Command, Communications, and Intelligence (C3I) and nuclear forces, primarily the threat posed by Soviet mobile ICBMs.  This left large conventional warloads as as a secondary mission only.  The design requirement were changed halfway through the program to provide for low to medium altitude penetration of a target due to reservations amongst the Air Force leadership on the effectiveness of stealth at that time, altering the size and payload requirements of the aircraft.
The Politics of Stealth: During the 1970s and early 80s when Low Observable Technology (LOT) was in its infancy, the military leadership did not fully understand its potential or the effect it would have on future air warfare.  Instead it saw the technology and envisioned stealth aircraft as a sort of Delta Force type weapon; the USAF would maintain a select few - and highly classified - squadrons of stealth aircraft to strike specific high value C3I targets, blinding the enemy while he was rushed by large and overwhelming conventional strike aircraft.  As such, stealth aircraft were not going to require the carriage of a lot of munitions for the task; this was more clearly seen in Lockheed's Senior Trend project, the airplane which became the F-117 Nighthawk, which only carried two large bombs for a payload.  The philosophy can't be argued too much with; we decimated the Iraqi military with a similar strategy in 1991 during Operation Desert Storm.  But it ignores the reality of air warfare today where non stealth aircraft simply aren't survivable in an advanced IADS environment.
Smaller Bombers: At the time of Senior Peg/Senior Ice, the USAF Strategic Air Command (SAC) had begun a shift in philosophy from large intercontinental bombers toward smaller fighter bombers such as the FB-111 for its nuclear delivery needs.  The strategy had several advantages to it.  Smaller bomber were much cheaper and could be procured in larger numbers for a given defense budget.  Second, they were cheaper to operate and maintain, and thus could log more flight time and have better mission readiness than their larger counterparts.  Third a large force of smaller bombers was more resilient to enemy defenses, if only by means of attrition.  This design philosophy is very apparent in Lockheed's Senior Ice proposal and possibly had considerable influence within Northrop on its Senior Peg ATB proposal, which became the B-2.

I wonder if "The Politics of Stealth" should rather be "The Strategy of Stealth".

There is another possibility - Neither the B52 nor the B1 has had information on it restricted to the degree that the B2 has.
It may well be that the B2's actual payload is quite a bit higher than has been publicly acknowledged. A great deal about that aircraft is still considered highly classified.

We know (or can reasonably estimate) the size of its bomb bay, though. Unless it's hiding another super-duper top-secret one elsewhere in the airframe, decent conclusions can be made on its capacity versus something like the B-52.

No, you have only seen what has been deemed acceptable for public release. There are numerous examples of military items whose true capabilities have been kept secret long after the item itself was shown in public, as a potential unpleasant surprise for an adversary. For decades after its launch, the true top speed of the passenger liner/potential troop ship SS United States, around 45 knots, was kept secret, as a surprise for a potential USSR invasion into Europe. To this day, the top speed of a LA class submarine, or the maximum diving depth of an Ohio SSBN are still kept secret.

You can do a Google image search for "b2 bomb bay" (example result) and get a pretty good idea of its dimensions, and accordingly, a decent estimate of its capacity. It's also quite clear that it doesn't have external hardpoints like the B-52. Top speed (and diving depth) is much easier to keep secret - you don't peel out of a harbor at 45 knots where everyone can see you.

And when those dimensions were shown publicly, they didn't put panels in place to disguise the true capability, like they do when releasing photos of cockpits or weapons stations in classified aircraft, or control rooms of classified submarines? Our government may be dumb, but our military is pretty good at keeping things secret, or even misleading a potential adversary, when it comes to the capability of a highly classified piece of equipment.

Look, if you want to take that approach, M-16s could have top-secret killer lasers and C-17s might have a top speed of Mach 20. Or we could just keep the conversation in the realm of what's likely. There is minimal benefit to lying about the payload capacity of the B-2 - modern wars aren't won on raw payload tonnage in this era.

M16's and C17's are not guarded closely. B2's, as the nation's premier high tech bomber, is very closely guarded, as releasing its full capability can have a direct effect on the nation's strike ability. If you think an M16 is the same as a B2, and that everything that can be known is found on wikipedia, complete and totally accurate...

It is highly unlikely that the B-2 has a secretly larger bomb bay. Simple as that. There's no logic behind your conspiracy theory, and other posters have provided perfectly rational explanations for the difference (lack of external hardpoints being a significant one). I'm done here.

@ceejayoz You seem very dismissive of the possibility that Doctor Who has provided us Time Lord technology.

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Do pilots have separate volume knobs on the radio panel?
I have about two hours in a Cessna 172 so my instructor always managed the radio for me. I found it too loud at some times and too quiet at others. Can I tweak mine without bothering him? I forgot to ask last time. Is this the same for most / all planes or does it vary a lot?

Do you have a G1000 glass cockpit?

I believe it’s a G500

Some modern audio panels allow for independent volume control for pilot (left seat), co-pilot (right seat) and passengers.
For example, a popular panel, the Garmin 340 has controls on each side of the panel, left for Pilot, right for Co-pilot:

Another popular panel, the PS Engineering PMA-series only separates out the Crew from the Passengers. In that case, you'd want to use your headset volume control (see below)

There are a lot of audio panels out there, so you'd just have to see if the one in your airplane supports independent volume controls.
Additionally, there is a difference between the intercom (in-airplane communication) and radio (airplane-to-communication frequency) volume controls. Often the panel handles the master volume (the mix of both intercom and comm) volume.  Whatever radio you're using (see below for an example using a popular GPS Nav/Comm the Garmin GNS430) will likely have a volume control for the Comm and Nav functions (the Nav - to listen to the audio broadcast from a NavAid).  In this case, I set the volume I like on the audio panel and then adjust the Radio volume after.

However, I think all (or 99%) of headsets have their own volume control, either inline on the cord or the adjustment is on the ear cup, so you can always adjust your own volume that way if the audio panel doesn't support it.

Inline and ear cup.
Related to all this is the question "what does the squelch do?"  Essentially the squelch is the volume threshold needed to activate the mic (notice how you don't have to push a button to talk within the airplane?). If set too low, the noise from the engine will continuously activate the mic, set too high and it won't pick up your voice even if yelling or with the mic close to your mouth. It is usually adjusted by either an outer ring (look at the little diagram on the Garmin 340 where it says SQ), or in the case of the GNS430, you push the volume knob in to adjust it. Other equipment, you pull the knob, so it's really a matter of getting to know your avionics!  A friend of mine once said, what you really need to know to fly a plane, is how to work the radio!

Thanks! Didn’t know about the volume on the headset. They have us using some old DC’s.

Yes you can, on your typical training cessna or piper the intercom and radio volumes are separately controlled. The radio will have its own volume knob and the intercom will have another, like this:

If the radio is fine but the intercom is too loud then turn down the volume on the intercom, and vice versa. If they're both too loud turn down your headset's volume control if you have one. Work with your instructor to find a balance that works for you both.
The other intercom knob is the squelch, and is worth mentioning. If the squelch is too low then you'll get a lot of engine noise in the background, if it's too high then you may not be able to hear yourself. I turn the squelch until the engine noise disappears then then just a bit further.


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Why don’t airliners have temporary liveries?
For buses, it’s quite common to have plastic foil with advertisements on them, but I’ve never seen that on an aircraft. Looking at how aggressively some airlines try to save money, they probably already came up with the idea to sell the space on the side of their aircraft for advertisement purposes – so why did they not do it? Is there any technical reason to not have temporary liveries?

related: How often is a passenger jet aircraft painted?, and Why is most aircraft livery painted, rather than vinyled?

They do have temporary liveries. This is very common in wet lease operators, where an aircraft is flown for an airline during a peak period or when their planes are down for maintenance. Airlines want customers to feel they are getting the brand-name product they are paying for; they don't want customers to board a generic white jet.
An airplane will be painted and decals applied only for several months. Just like motor vehicles, 3M makes aircraft film wraps, including models specifically for short-term use.
It is also common to have a livery for a special event, say the Olympics. You can expect ANA's jet for the 2020 Tokyo Olympics to be returned to normal shortly after the Olympics are over. You can see Lufthansa and Egyptair dressed their planes up for the World Cup. Egyptair's photographic livery can only be done by printing onto a decal.
This video shows Alaska Airlines paint essentially an ad for Disneyland and the Cars movie franchise. They paint the simpler parts like the clouds and the large solid areas, but at 1:28 you can see them apply decals of the characters' faces. They say it took 29 days to paint. This is another video where they're simply applying a decal to advertise another movie.
So, no, there is no technical reason not to have a temporary livery and such schemes are done regularly. It's merely an issue of marketing and customer impressions.

Granted that it's been quite a while since I've flown commercial, but I don't recall getting more than a brief glimpse of the outside of the planes I was actually flying in.

@jamesqf For a lot of marketing messages a brief glimpse of a bright passing ad from the departure lounge is all you need, very simple messages like "there's a new movie with these characters", "visit Disneyland", "this airline flies our national soccer stars", similar to billboards on a highway. Looking at bus ads, many are the same way.

@jamesqf me too, but in some airports you can end up sitting in the lounge with a clear view of your plane for quite a while (Madrid for example)

@jamesqf And it doesn't have to be the plane you (the viewer) are flying in. The ad can usefully reach anyone who happens to see it through a window from the terminal, or while taxiing in a different plane -- you might never board the plane with the ad, but are still part of its audience.

The time needed to apply and remove the advertisements would cost too much money. As long as the aircraft is on the ground, it cannot earn revenue. Better to forgo the small profits from ads for larger profits from operating the aircraft.

The time is the crux.  Painting a vehicle is slow and laborious, and the advertiser must pay both ways: to paint and paint back to original... so such adverts are printed vinyl wraps that can be thrown on quickly.

@Harper, between the huge fixed costs, the small fraction of time people actually see the aircraft and the higher durability of the foil and glue it still does not seem to be worth it for common adverts—and it is occasionally done for a publicity stunt.

The "publicity stunt" is probably the most important aspect - a few thousand people may see the aircraft, millions may see it indirectly reported on television or social media.

@Harper Not just paint back to original - I would assume they'd also have to remove the old paint before applying new paint.  Paint might not weigh all that much, but if you keep adding layer after layer, it adds up, and also I'd imagine it would start gumming up the works after a few dozen repaintings if you don't remove it in between...

1) For a typical urban bus, that plastic foil has to stay on at maybe a max of around 60 mph.  For a commercial jet, it'd have to stay on at 600 mph.  And suppose it starts ripping off and gets tangled in the elevator...
2) You could repaint the plane at a cost of $50-200K How much does it cost to give an airliner a fresh coat of paint? but the ad would only be seen by the small number of people at the airports, so hardly cost-effective.

If the ad is well-designed, it can also be seen by thousands to millions of people who live under the entry and exit lanes of airports.

Building upon jamesqf answer, I'd like to add:
3) The number of people seeing bus on the streets while moving between stops could be simplified as sum of traffic size + population working and living along its route. For every bus you get a very rough estimate of a thousand potential advertisement targets every minute. And who sees the plane? Only its passengers when they're boarding. People waving their goodbyes usually are too far to read the advertisement, not to mention ppl seeing the plane inflight. That amounts to one to several hundred advertisement targets per several hours, or even whole day in case of longer routes.
The increased cost leads to a fraction of market penetration. Totally not worth it.

They have been using temporary liveries for decades.  Rock group Yes famously had one produced on film for their US tour in 197x and half way across the Atlantic it started peeling off and flapping towards one of the engines.  YouTube for Rick Wakeman telling this story as he does it so well in his inimitable style

Also Iron Maiden's Flight 666.

@Graham I think they called pretty much all of their flights "flight 666." For example, since they're leasing a 747 from Air Atlanta Icelandic, their callsign is "Atlanta 666" in all of the cases where I've heard of it. They informally call their aircraft "Ed Force One," but I doubt ATC would let them use that callsign. I can just imagine: ATC: "Air Force One, be advised, similar callsign on frequency." Air Force One: "Say again??"

@reirab "Wait, is it Iron Maiden? OK. We'll be Air Force Two."

Part of the reason is branding. A city bus is a city bus, but an airline wants to advertise its own brand with its own livery. Some people dislike ads, so that could create a negative perception of the airline.
Part of the reason is cost. An airplane is much larger and more expensive to have out of service.
There's also lower benefit. Buses with advertisements spend most of their time in the city and on roads, surrounded by people they can advertise to. Airplanes spend most of their time in the air, where nobody else gets close enough to see them very well for very long. They do get some exposure near the airport as they are landing or departing, and to people in the terminals.
However, some airlines do put advertising on their planes. It's usually something with a connection to a flag carrier's country, as with Air New Zealand and The Hobbit, or a partner of the airline. Airlines will commonly have some aircraft painted in a livery of their alliance. ANA has had many special liveries, such as Star Wars and Pokemon. The airline tries to make it as appealing as possible, because in addition to advertising something, they are also drawing attention to their own brand.
There are certainly outliers, though. Ryanair is famous for eking out every bit of revenue that they can come up with, and advertise throughout the cabin. They have a history of advertising on their planes, and did announce in 2013 they would be selling advertising space on their planes, but I couldn't find any recent examples other than partners.

"A city bus is a city bus" That depends on where you are. In the UK, city buses are run by private companies, and they still carry ads.


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What are possible causes for the flaps not deploying on a Cessna 172?
I would like to seek some expert opinion on why my flaps failed to deploy when I took it to Flaps 20.
I was turning from Downwind to Base when I took flaps 20 and noticed that my speed was creeping past 80kts even at idle power. My instructor took a look outside and that’s when we realised that the flaps were still at the UP position. We tried checking the circuit breaker for Flaps and the other switches, and everything else was normal.
We came in flapless until short finals when the flaps deployed to Flaps 10 when the switch was moved to the Flaps 30 position.
We did some checks on the ground and whenever we took Flaps down, static interference could be heard. It’s as if it was timed to happen the moment the flaps are extended. No static heard when the flaps are raised.
Any expert opinion would be appreciated as I would like to really understand what I am flying. I have checked the POH and it barely says anything, even the Electrics diagrams aren’t helping me diagnose why.
I’m a student pilot with barely 20 hours flight time.

ATIS on that day was: Temp 39 with M12 Crosswind. QNH1010.

So flaps anything 20 or less gave you no flaps at all, but once you selected flaps 30, you got what you should have had by selecting flaps 10? Did you hear static also when raising the flaps? Was the static related to the switch movement, or to the flaps movement?

I'm definitely not an expert on the C172, but for me the flaps switch (control) and the cabling all the way to the flaps actuation motors would definitely be a prime suspect along with whatever sits between the motors and the actual flaps...

@aCVn yes that’s right. The static noise only happens when the flaps start extending downwards. You could hear crackling noises that would be timed to happen at the same time when the flaps start to lower, as soon as you take a stage of flap.

@aCVn no static was heard when the flaps are being raised.

Please [Edit] your question to include that information.

What does youe mechanic say?

@vasin1987 I’ll check with them when they work on Monday.

Don't fly it like that, the aircraft should be taken out of service. The last thing you want is sudden flap deployment or asymmetric deployment on short final.

@RonBeyer is the C172 capable of asymmetric deployment? I figured both sides were mechanically linked.

@AEhere Yes, it is possible. The flaps are connected through pulleys and wires through turnbuckles and are mechanically linked, but if one is jammed and the wire breaks, one flap might work, and the other might not. Since the flap motor is in the right wing, it would be more likely that the right flap would work, and the left would not. Here is at least one case of it happening

@RonBeyer TIL. Thanks for that, I can make it into a proper question if you feel like elaborating.

@shogunnyan any feedback?

@vasin1987 negative no fault found :/ back into service and flying normally somehow

If the flap actuating motor is defective, you'll get exactly (or very close to) those symptoms, including the "interference" when the motor is operated. It could also be that the power connector to the motor was loose, damaged or corroded.


text:
Where can I find the German GAFOR online?
Where can I access the GAFOR for Germany for free online (or at least something close)?

You can find all the free aviation weather services of the DWD here:
https://www.dwd.de/DE/fachnutzer/luftfahrt/teaser/luftsportberichte/luftsportberichte_tabelle.html


text:
Where can I find VFR approach charts for Italy?
Has anyone a good source of free information for VFR approach charts in Italy? I know that for major airports (e.g. LIMW), https://www.enav.it publishes the charts.
However for small airfields (e.g. LIVV), I was not able to find anything. I am looking for something like this, from France.

You are right, in Italy, VFR approach charts are published by ENAV for major airports only (you could get them georeferenced for free using Airmate app). For small airfields and ultralight bases, the main source is  Avioportolano but it is a commercial source. There is no free information source to the best of my knowledge.
In France, the source you quote SIA Service de l'Information Aéronautique is indeed the right one for all airfields having an ICAO code assigned. In addition, you have more than 700 ultralight airfields having numeric codes assigned by the ULM Federation (such LF8357 for Pampelonne). You could find for them free information and charts on FFPULM BASULM site.

I can recommend two free solutions which are using the official government (ENAV) issued charts:
openaip.net
openflightmaps.org
Openflightmaps is maintained by the University of Graz:

The mission of the project is to develop and maintain a universal
database of aeronautical data, in order to facilitate the rendering of
high quality VFR maps to assist the general aviation community.

You can generate pdf exports for kneeboard printouts or iPad reference easily:


text:
Is there a local UAS code database?
Has anyone created (or proposed) a database or clearinghouse of local and state codes, restrictions and prohibitions applicable to UAS?

Why revert the edited title?

@JimyPP the proposed change was much wordier and did not substantially add to the question, in my opinion.

@mongo, we tend to prefer actual questions in the title, so Jimy's edit was according to our guidelines

So far no one has created an official database. By official I mean one that you can count on to be correct and up-to-date. There are a few people who have created databases, but they all come with the caveat that they don't guarantee the info is correct and current.
The thing is, I don't really know if you could create a reliable database with the laws the way they are. A few states have stepped in and written a preemption against local ordinances, so in those it would be fairly easy to do. But in other states there'd be no way to keep up with ordinances enacted by the the thousands of county and local governments, many of which don't maintain an easily-accessible method of publishing their laws, and most of which are written by people who know little about uas, so the laws are often very vague.
The laws are also changing quickly right now, creating an untenable situation for drone operators. The US Senate is currently considering a bill that specifically legislates against any possible fix to this situation. It's really a complete mess.
A few of the databases I have found are:

Jonathan Rupprecht Law Office database
National Conference of State Legislators
Drone Law Today State drone law reference book

One town in NY has a collection of laws, which even the town office could not assure they could identified completely.  Some were published in the town code, and some were in town board meeting minutes.  There is no index for that town.  Complicating things, they have a stadium, which has it's own TFR and NOTAMs.  Further complicating things, while there are area wide bans, there is a provision where a landowner can fly over his/her property.  Sounds like things are ripe for another Singer v Newton.

@mongo Yeah, that's a mess. I don't see how people are supposed to deal with stuff like that. It's going to be everybody's knee-jerk reaction to just ban them everywhere. I understand the need for local rules. You shouldn't be allowed to fly your drone over your neighbor's house and spy on them. But there has to be clear guidelines on what they can and can't legislate locally. Much like driving. There are some differences in ordinances here and there as to what's allowed But the entire set of driving rules don't change when you go from one city to the next.

I received an email, with a news article. It seems that someone flew a UAS and got charged with trespass with an unmanned aircraft. In Sept 2017.


text:
How does a Machmeter behave if the static port is blocked during a constant CAS climb?
Question: How will the machmeter behave in a constant CAS climb if  the static source becomes blocked?
Answer: The machmeter reading will decrease.
Why? I couldn't find any logical reason for the machmeter reading to decrease. My understanding is that when CAS is constant during a climb, the TAS should increase. If the static source is blocked, this will only increase the TAS further to maintain same CAS because the static pressure outside is less than the pressure in the blocked static source.
I fail to understand how the local speed of sound (LSS) is related to a blocked static source. Because LSS is related to temperature only, so it decreases during a climb.
That means that Mach speed = TAS (increasing) / LSS (decreasing) = overall increase in Mach speed
What am I missing?

If you have a constant speed climb, the total pressure measured by the pitot tube would drop, thus the indicated speed would decrease, not increase. Could it be a misinterpretation that "constant CAS climb" means an autopilot constant speed climb (not an actual constant CAS climb)?

If your static port is blocked, you have bigger problems than the behaviour of your machmeter.

A pneumatic airspeed indicator relies on the differential pressure between the pitot tube and the static port.  If the static port ices over, as an example, the altimeter will read constant, and VSI will become zero.
Assuming the pitot tube is operational, an increase in altitude will result in a decrease in ram air pressure measured at the pitot tube.  This will result in decreasing IAS.  Since most machmeters use air data from the static and pitot system, the machmeter will also show a decreasing mach number.  Practically speaking, the IAS and machmeter will become rapidly unusable with an obscured static port.


text:
What is the correct technique for working on an airframe with a pneumatic rivet gun?
I currently work as a trainee AME and want to eventually start specialising in sheet metal / composite repairs as I've heard the money is really good for these specialist skills. I've bought myself a pneumatic rivet gun to start practicing some basics and have an array of sets for the rivet sizes and types.
My question to any aircraft structural engineers / experienced sheet metal workers in this forum is how to stop getting the smiley faces on the solid universal rivet head? I'm putting enough pressure on the gun to stop it bouncing and the bucking bar is setting a good rivet tail but on some of my rivets I have this smile crease / dent at the bottom of the rivet head. Does this mean the gun isn't in line enough with the rivet? I'm always trying my best to keep the gun 90 degrees to the sheet metal. Or am I doing something else wrong? I've been told I'm using the correct set and air pressures so I'm sure it's my technique letting me down on some of these rivets. Although less mistakes are happening when I get someone to hold the bucking bar so I can use two hands I still have the same smiley face problem on some. Any tips and tricks would be much appreciated.

I banged rivets on a production line in a previous life (in the 70s). A trick that works wonders (although it may be frowned upon by purists, and your school instructors may prevent you from using such a "cheat" while learning) until you get good at holding it perfectly perpendicular is to put a little piece of masking tape over the tip of the rivet snap.  It moves the snap a few thousandths of an inch away so that more misalignment is tolerated as well as putting a barrier between the edge of the snap and the skin surface if it does touch.  You will find your smiley rate goes way down.
I tried to draw a little picture of what I meant in Paint but I couldn't do it without it looking like a rude bathroom stall drawing, if you know what I mean...
The other thing I see people doing is just shooting it full blast, then off.  Don't do that.  The gun has a "feathering" trigger that lets you ease in the air for a reason.  When you start to set the rivet, ease on just a bit of air, just enough to get it ratatatatting, and feel for the feedback of the bucking bar on the other side to tell you you have good contact, then give it a full shot.
Each shot should sound like, "ssstat tat tat tat tat tat brrrrrrrrrrrrrrrrrrrrrrrrr".
Especially when you have a partner bucking, you'll know right away if they don't have the bar in place on the shop side.  This helps prevent depressing the metal around the rivet, as well as reducing the risk of smileys.
Another one is don't hold the rivet gun by the handle like a pistol.  You have to be able to push in line with the snap.  Old time rivet guns were made U shaped for this purpose, but all the modern ones have the terrible pistol shape.  Move your hand as high as possible so you are pushing with the heel of your hand on the back of the rivet gun's body, with your wrist more or less in line with the snap.  Your index finger will be too high, so use the middle or second last finger to work the trigger. Like this:


text:
What is the total wing surface area of the A320?
I was trying to calculate the total area of an A320, and in this link I found the wing area and tail area. But here I read that the wing area is just the 2D projection of the wing. So if I wanted to calculate the total surface of the wing I should consider the wing area (122.4 m) and multiply by two, which would be an approximation.
By doing this, and considering the fuselage to be a cylinder, I get a total area of 847 square meters for an Airbus A320, which is close to the 900 square meters reference I found in this article.
So, is it correct to say that the surface area of a wing is approximately the wing area multiplied by two?

As I'm not sure whether you were only looking for the methodological answers provided earlier, this is a more detailed answer to the calculation problem you were trying to solve in the first place, providing an answer to the question posed in the title of your question. It is based on the A320 Airport and Maintenance Planning Manual, which provides approximate dimensions of the aircraft.
For the wings and wing-like surfaces, details are as follows:

Wing top surface: $99.7 m^2$ (excluding wingtips devices)
Wingtip devices (normal, non-sharklet A320, both sides): $1.8m^2$
Horizontal tailplane top surface: $27 m^2$
Vertical tailplane (both sides): $43 m^2$

Counting horizontal wing and tailplane surfaces twice (upper and lower), that yields a total of $298.2m^2$. This does not properly account for thickness (using the factor $1.07$ mentioned by Daniel yields $319.074 m^2$) and movables (high-lift devices, control surfaces, etc).
For the fuselage and nacelles, only top surfaces are listed. Modelling these as simple cylinders therefore seems the best way to go. Based on a fuselage diameter of $4.14 m$ and a length of $37.57m$, that yields a surface area of about $488m^2$. Of course, the fuselage is not strictly cylindrical, but I'm assuming here that is offset by the fact that I'm not explicitly including the front and rear surfaces (of a closed cylinder). Nacelle dimensions are not specified (probably as that somewhat depends on engine type), but based on drawings, I'm estimating a length of $5 m$ and a diameter of $2.5m$, resulting in a total surface (again: cylindrical approximation) of $78.5 m^2$ for the two engines. For the pylons, lets add another $5m^2$ per side.
In total, that adds up to $872 m^2$ (or $902.874 m^2$ with the 1.07 thickness approximation). That corresponds nicely with the $900m^2$ you found online - and also shows your own calculation wasn't too far off (some 3%).

The answer depends on the method used.
For airliners, the two most important methods are the Wimpress and the Airbus method (the Wimpress being used by Boeing). The difference is the triangles you get by extending the wing's leading and trailing edges forward into the fuselage for Wimpress versus connecting the points where the leading and trailing edges meet the fuselage on both sides by two straight lines for Airbus. This discussion on airliners.net lists a comparison of the wing areas you get with both methods for a range of models.

Wing area methods in comparison. The shaded are is covered by the fuselage and determined differently; creating different areas for the same wing.
Note that the specifics of the method used is irrelevant for the purpose: This wing area serves as the reference area of most aerodynamic coefficients and either method is good enough for the purpose. Consistency is more important than precision here.
Both methods use the projected area of the clean wing in the x-y-plane, because that is the area relevant for lift. Divide by the cosine of the dihedral angle if you feel the projected area is not good enough.
For the wetted area you need to subtract the fuselage, divide by the cosine of the dihedral angle and the cosine of the incidence angle, and also add a factor to account for the wing's thickness. For this, the approximation $1 + 2\cdot\delta$ has proven to be useful, with $\delta$ being the relative thickness of the wing. And then, of course, you need to double that result in order to account for both sides of the wing.
One of your links calculates the area of a wing that needs to be painted: This should include the forward section of the Fowler flaps which are covered by the spoilers in the clean configuration.

Could you explain what you mean about the forward section of the Fowler flaps being covered by the spoilers in the clean configuration? I'm having a hard time visualizing that.   Thanks!

@RalphJ If you imagine to spray-paint the clean wing, you will only paint the rear part of the flaps. Now set the flaps to fully extended and you will see that their forward section is unpainted, because it was covered by the spoilers and rear wing structure.

As an addition to all previous answers, there are some more detailed estimation methods for the wing wetted area in literature. For instance, here's a method by Torenbeek (1976):
$S_{wet} = 2S_{exp}\left(1+0.25(t/c_r)\frac{1+\tau\lambda}{1+\lambda}\right)$
Where $S_{exp}$ is the exposed part of the wing reference area, $\lambda = c_t/c_r$ and $\tau = (t/c)_t/(t/c)_r$. Note that the root is taken as the wing-fuselage intersection in this case. These kind of methods are especially useful when estimating aircraft parameters such as the drag coefficient using statistical values given by a certain author (Torenbeek, Raymer, Roskam etc.), since these values were derived using certain definitions of the geometrical parameters.
Another more simple method (I can't find the source anymore) suggests $S_{w_{wet}} = 1.07 * 2 * S_{w_{exp}}$. The factor of 1.07 is added to account for the thickness of the wing.

Wing area is usually expressed based on total span x chord, including the area covered by the fuselage.
The fuselage is given a bit of credit as a semi-lifting body.  There is a similar credit-for-lifting-body effect when you add floats.  The floats generate enough lift, or almost enough lift, to support their own weight, so when floats are added there is usually a fairly small reduction, or sometimes no reduction, in useful load.
Same with the fuselage itself, so the area of fuselage between the wing roots is assumed to be part of the total wing area.  Hence total span x chord (or mean chord for a tapered wing, based on the taper extended to the fuselage centerline).


text:
Does the US export the Mark 77 aerial bomb?

The Mark 77 bomb used by US fighter aircraft detonates with an impressive array of inferno when dropped in a cluster which is often done at airshows.
Questions

Is the Mark 77 bomb solely used by the US air force only, or has such ammunition been exported to other countries? Even the typical delivery platform, the F/A-18 Hornet has been exported to a few countries military. According to Wikipedia, it seems like there are no foreign operators of this munition. (given that this is older technology, there is no need to hide its mechanics, and that ammunition usually comes as a package deal with the aircraft)
Are there any Russian, Chinese or foreign manufactured equivalent bombs (guided or dumb) capable of that sort?

EDIT: I know of US's MOAB and Russia's FOAB, but I would like to know if other countries have conventional incendiary bombs

I always thought airshows simulated these sorts of things using ground-based pyrotechnics - nothing is actually dropped.  Something about safety and not bombing the audience by accident.

Ok, but that still doesn't hides the Mk 77's capabilities in a real war or exercise

@DanPichelman not to mention cost.

Mark77 is a barrel of kerosene. Many nations recognized that dropping flaming stuff on people tends to kill or maim - For a list of (suspected) users besides the US: https://en.wikipedia.org/wiki/Napalm

https://citeam.org/new-evidence-of-russian-incendiary-bomb-use-in-syria/?lang=en

MOAB isn't an incendiary: it's designed to explode, not burn.

@DanPichelman The perfectly straight line also strongly suggests pyrotechnics on the ground.

I cannot find any info on the export status of the  Mark 77 with a routine search, and plenty of reports of media attention to its use, which leads me to believe there is not a huge market for it among US allies due to the potential for negative press.
For your second question, the Russian equivalent are the ZAB-xxx series of bombs, where the acronym stands for incendiary airdropped bomb (Zazhigahtel'naya Aviabomba) and the number is the warhead weight in kilograms. It seems the most used version at the moment is the ZAB-500. Variations include the OZAB and OFZAB, where the O is for fragmentation (Oskolochnaya) and the F for high-explosive (Fugasnaya). I have not been able to find a link with info on the  OZAB version.

Similar munitions sometimes come with an RBK (Razovaya Bombovaya Kasseta) prefix, meaning cluster dispenser, for example RBK-500-ZAB, which is a standardized RBK-500 cluster dispenser with over 100 ZAB-2.5 incendiary sub-munitions, for an approximate 500kg of combined warhead mass.


text:
Do stealth designs have canard configuration?
Do stealth-focused aircraft have canard configuration? I believe canards have a negative impact on the radar cross section.

"stealth designs" is rather broad. Aircraft like the Rafale and Typhoon incorporate stealth features, but are not optimized for stealth at the cost of all else. The F-22 and F-117 are more stealth-biased than Rafale and Typhoon.

I think @NitinG is referring to stealth-focused designs like the F-22 and Su-57.

So far, no operational stealth aircraft has had a canard wing as the canards do affect the radar cross section.
However, a few experimental and under development under development aircraft have canards, like the Chengdu J-20.

"J20 2" by V587wiki - Own work. Licensed under CC0 via Commons.
The Sukoi PAK-FA, on the other hand uses movable Leading Edge Root eXtensions(LERX), which are much more stealthy and are shown drooping down in the following figure.

Source: defenceindustrydaily.com
There are a few major drawbacks with the traditional canard designs:

Planform alignment Most of the canards are in aircraft for stability and aerodynamics requirements an as such are not amenable to planform alignment, as their characteristics are sensitive to their shapes and sizes. For example, compare the planform alignment in case of F-22 and Eurofighter Typhoon.

Source: forum.keypublishing.com
Some low observable aircraft, like the Boeing X-36 did  have planform alignment, it is simply that it is difficult to achieve.

"McDonnell Douglas X-36 planform" by NASA/Dryden Flight Research Center - http://www.dfrc.nasa.gov/gallery/photo/X-36/HTML/EC97-44165-151.html. Licensed under Public Domain via Commons.

Canard Angle Most (not all) of the canards have an anhedral or dihedral due to aerodynamics requirements, which means that they are not in the same plane as the wing and reflect radar waves in other directions, increasing RCS. The following image shows the (mis)alignment of canards with the aircraft.

Source: forum.keypublishing.com

More reflecting surfaces Having canards basically means there are two extra surfaces to reflect the radio waves and increase RCS.
Interaction with fuselage and wings The diffracted (radio) waves from the canards can impact on the wings and fuselage and get reflected back, which can increase the radar cross section.

The comparison between F-22 and EF-2000 (or the other canard designs) is not really fair. F-22 was specifically designed for stealth and the angles were adjusted to match while in all the other designs the angles were left at whatever made most sense aerodynamically. It does not prove that adjusting them would have higher aerodynamic penalty in the canard case than in the horizontal tail case.

@JanHudec which is what I'm trying to say- aerodynamic and stealth requirements don't (usually) match.  Though we may never know the trade-off (between stealth and aerodynamics), there are some hints- The Chines dropped the canards in J-20 in their (next) stealth aircraft, the J-31 and the Russians moved from canards to LERX in PAK-FA, while maintaining the maneuverability from Su-30

I agree with most of the answer. I just say the particular image is misleading, because the mismatch is there for both canards and horizontal tail. It is not like Lockheed switched away from canards to conventional tail when designing F-22; none of the earlier US fighters uses canards either.

@JanHudec I think I see your point. I just wanted to point out the importance of planform alignment and its effect on using of canards in stealth aircraft; I wasn't trying to compare two aircraft with different stealth requirements.

Would u mind editing in a quick sentence or a link to define "planform alignment?" Although the diagram indicates it I had to go look it up to make sure I was understanding correctly. I found this on the web: "Planform alignment is a technique for reducing an aircraft's radar cross section by orienting all the flight surfaces of the aircraft at the same angles."

@JanHudec - I think the difference is that the main use of stealth is to mask an aircraft's approach, so the aircraft has to be stealthiest from the front. Canards, being in front, thus make it that much harder to achieve this goal. As an aside, the YF-23 that lost the ATF competition to the F-22 was actually the stealthier aircraft in competition testing, in part due to its "rudder-vater" configuration that reduced the pure horizontal surface area (though at the cost of reduced maneuverability to the Raptor).

@KeithS, I don't think there is much difference as long as the surfaces are same size, horizontal and properly aligned. Yes, ruddervators can have advantage for stealth and they can't be canards, because unlike elevators, rudder ahead of C/G is not practical.

Canards can be stealthy. There is a very interesting Oregon State University lecture given by Dr. Paul Bevilaqua about the F-35 that actually shows a canard fighter.

The point here is that you use computer models to optimize radar return, especially to the front but also to the rear. A fighter that doesn't look optimized might still be.

Welcome to the site. Link-only answers are generally discouraged here to combat link rot. It would be preferable if you'd explain in your own words what is the main point being made in the linked video.

<Result: [..]> what does that have to do with the question?


text:
How did the De Havilland Mosquito compete with contemporary jets?
During the Second World War, the British De Havilland Mosquito light bomber achieved success in raids through its sheer speed. Traveling at up to 392 mph, it could outrun virtually all piston-engined interceptors, removing the need for it to carry defensive weaponry. Later in the war though, German jets like the ME-262 could travel at speeds in excess of 500 mph, seemingly making the Mosquito obsolete. How did the Mosquito compete with these jets successfully, despite the obsolescence of its only major advantage?

"Outrun" is a bit of a simplification; the Mosquito also had much better maneouverability than earlier light bombers (it was by no means designed for dogfighting but had more than just speed in its favour) example

The Mosquito was a great aircraft but it was not faster than Germany's Messerschmitt ME-109 and Focke-Wulf Fw 190 piston powered fighter aircraft.
It also did not successfully compete with the jet powered Messerschmitt Me 262. The limited numbers of ME-262 were probably the only reason the Mosquito could survive in the same airspace.
On 26 July 1944 the first aircraft to be shot down by a ME-262 was in fact a Mosquito: Mosquito Operational History
"a 262 A-1a, caught and severely damaged the Mosquito in a pursuit. The Mosquito, which managed to escape into cloud, later crashed at its destination airfield in Italy, and the airframe was written off"

If it made it home, did it really get shot down? :)

I think it's considered shot down in the damage done resulted in the airplane not being usable anymore.

Actually the Mosquito was faster than the BF109 (~400 to 450 mph vs 379 mph) and barely faster than the FW-190. However it was able to fly far higher than either, unless the german aircraft were specially modified for high altitude intercepts.

It is difficult to directly compare aircraft performance because there are many variables. (operation weight, operational altitude, external stores, etc.)  I have never heard of a 450 mph Mosquito (415 mph is the usual quoted top speed and the ME109K had a top speed 440 mph)    http://www.wwiiaircraftperformance.org is a great resource for researching WW II aircraft performance.

The account http://www.mossie.org/stories/Norman_Malayney_2.htm gives a good description of the speed during the combat with a flight of ME-262's

There's a pretty good account of two of the early encounters between photo recon Mosquitos and an ME-262 at this link: http://www.mossie.org/stories/Norman_Malayney_2.htm
In both cases while the ME-262s were about 50 mph faster than the Mosquitos, because the Mosquito was much more maneuverable than the ME-262 both survived.

Welcome to aviation.SE!

By the time that the ME-262 became operational, there was a huge lack of fuel, oil and resources in germany. They also lacked trained, experienced pilots. This means that missions in the ME-262 were limited, and they did not usually go up to shoot down photo-recon mosquitos. Instead the ME-262 and other german fighters of the time were reserved for anti-bombing missions were they tried to shoot down enemy bombers. This means that encounters between the Mosquito and the ME-262 were not that common, and if they found each other, the ME-262 would usually win.

the first encounter between the Mosquito and the Me262 was reported by the Mosquito crew (Wall and Lobban) on 25th of July 1944, while the Me262 pilot Scheiber reported the encounter on 26th July 1944.  Scheiber reported the Mosquito as a kill but the the latter survived and landed safely at a friendly base in Italy.
available records do not specify if said Mosquito was able to operate again, but damage was described as non-lethal.  the navigator did mention that the "outer dome" was blown out, but if it could fly from Germany to Italy then likely the damage was not enough to warrant a kill.  it probably flew again.

Welcome to Stack Exchange. It would improve your answer if you could include some sources for the information you've provided.

Proper capitalisation of sentences would also give a bit more credibility.

see my above comment, but there's the link
http://www.mossie.org/stories/Norman_Malayney_2.htm
BTW your credibility could be much enhanced without the snark @Transistor

@Larry: It's not a snark. It's an encouragement to write properly as is recommended on most of the SE sites. Bad writing makes the posts difficult or confusing to read and reflect poorly on the author as well as lowering the overall quality of the SE sites. We make allowances if English is not a first language but there is nothing in the user profile to indicate this (and all European languages use capital letters at the start of sentences).


text:
What would happen if flaps are extended beyond 40 degrees?
The angle of flaps is limited to a specific value. It's around 30° to 40° on most aircraft what I've seen.

Source
But what happens when they get extended even further? 50°, 80°, 90°, ...
Let's also say they don't break due to high load on them. I just want to know it theoretically.
What will happen to the plane?

Will drag be increased?
At which point will the aircraft loose it's lift due to the extreme deformation of the wing?
What about the slats?
Are there any aircraft that use a higher than usual angle of flaps?

Are you asking if the flap mechanism broke? Or if designers actually allowed the pilot to extend them to those additional detents? What kind of flaps are we talking about here? Fowler flaps? Plain? Split? Slotted?

@RonBeyer I edited the question. I know, there are differences between the kind of flaps, but let's just talk about flaps in general, devices that create lift/drag.

Further extension makes the flap act like spoilers as there is no airflow attached anymore so they are basically acting as an air brake. The flaps in the picture are so called slotted flaps, here the slot ensures that the flow is attached to the flap, but even those flaps will eventually stall as the angle of attack to that section of the flap system becomes to large and the flow will be fully separated. The now fully disturbed air aft of the main wing will affect the controllability of the aircraft as "dirty" air is hitting the aft wings.

Note that 30°, 40°, 60° etc. are just for reference purposes. Look at the Boeing 777 inner trailing flaps, their deflection is quite pronounced (maybe 60 or 70°) Flaps are designed according to manufacturer's computations. There's no point in building flaps that requires excessive and heavy structural devices. However, some modifications can be done to allow a model to perform better on high and hot/short runways (eg: B737) The aircraft looses lift when airflow above the wing is disrupted : it stalls; extend the flaps even further and at some point (speed/AOA), the airflow won't cope anymore.

Depends on the kinda of flaps installed on the aircraft; in the example above with fowler flaps, the design would begin to just create excessive drag without gainful lift and would require a pretty bulky structure to accommodate for the aerodynamic loads imposed upon them.
Now some other types of flaps like the split flaps or dive brakes like those found on the Spitfire fighter were designed to extend 90°.

Those flaps must have an interesting effect on the exhaust from the radiators.

The type of flaps shown in your question (Boeing 727, right?) work because of the small gaps between the single elements. Those help to re-energize the flow, and if more are added, a steeper angle will be possible. Deflecting the flaps more without adding more elements and gaps, however, will lead to flow separation when the wing is kept at the same angle of attack.
This separation reduces the pressure recovery towards the trailing edge and adds more suction on the rearward-facing parts of the wing, so separation increases drag. But the deflected flaps will also block the flow on the lower side of the wing more, which increases local pressure and, consequently, lift. However, this lift increase is small and is bought with a massive drag increase, so it is not economical to increase the flap deflection angle.
Note that increasing the angle of attack when flaps are deflected will cause a gradual increase in flow separation, beginning at the trailing edge and moving forward as angle of attack is increased. While the flow over the flaps is attached at the approach speed and angle of attack, during the flare it will start to separate. The drag increase from this separation is actually desired because it helps to slow down the aircraft.
Less complex flaps do use higher deflection angles and the flow separation that comes with it on purpose. Take the SB-10, for example: Here the inner camber flaps can be set to 70° for landing. This setting will produce the highest lift coefficient, but the drag is excessive. With an L/D of over 50, the SB-10 is not easy to land, and the high drag helps!
A typical landing works like this: First, the approach is flown at 90 km/h with normal flap setting for low speed (+10°) in a glide pointing at a location far beyond the desired landing spot. In about 30 to 50 m altitude the pilot pulls the nose up and slows the airplane to 70 km/h so the dynamic pressure on the flaps is low enough to deflect them down to 70°. Then he has to push the nose down quickly to avoid stalling the glider, and now he can point the aircraft at a point on the ground maybe 50 m ahead of the desired landing spot. Pushing more will increase speed only moderately because of the high drag of the flaps (and the landing gear; it also adds maybe 50% of the drag of the glider with normal flap settings). Now the speed will be between 90 and 100 km/h and the flaps will create a loud whistling sound - great to alert everyone on the ground that the SB-10 is coming in for landing! In 5 m altitude he has to start a well-timed flare because speed will now decrease quickly and the aircraft will settle down immediately without any floating. Great for landing out in a restricted space.
Below you see the combined flap and speed brake which was used in the Glasflügel Mosquito and the Schempp-Hirth Mini Nimbus. Figure 1 shows the regular deflection range, while Figure 3 shows the approach configuration. Note that the segment ahead of the flap starts to open in order to act like a spoiler. While this increases drag, lift will be unaffected. Figure 2 shows the landing configuration which will produce the highest lift, but also the highest drag.

Flap and speed brake of the Glasflügel Mosquito.

I've always wondered, the FAA's Pilots Handbook of Aeronautical Knowledge describes the split flap configuration to be the most effective design, but I always intuitively though that the Fowler flaps would be a more efficient and effective design.  Since they would seem to produce the most drag and a lot of flow separation, why are they considered to be more effective?

@CarloFelicione: I agree, Fowler flaps create much more lift. I think the FAA handbook only compares flaps which don't increase wing area, and in this category the split flap (more precisely, the Zap flap) has the highest effectivity. In terms of lift and drag with the least mechanical effort, split flaps are top.

When flaps are extended beyond the standard 40 degrees the result depends on the design of the rest of the aircraft.
Extreme deflection of large full span flaps has been used experimentally to attempt to create STOL/VTOL aircraft, such as the Ryan/Fairchild VZ3. Flaps here are at 90 degrees and have huge end plates to reduce losses. A turbine in the fuselage powers the two props through a shaft drive. The exhaust is vectored out the tail to provide pitch and yaw control at zero speed.

Drag is extremely high, but if you are trying to hover this is not a bad thing since forward speed is not desired. In this test the aircraft sits at a high angle on its main gear and tail to reduce forward thrust. A bunch of people holding a rope are trying to help.

The amount of lift produced in a hover, regardless of wing, is no greater than the amount of thrust produced by the propellers. Lift is deflected airflow and no wing is 100% efficient, so this was abandoned to be eventually replaced by tilt rotors, where all the thrust produced does provide lift.

The aircraft will stall.
At some point, the drag created by these "panels" (now hanging more and more vertically) will exceed the maximum thrust of the engines. The airspeed will decrease significantly. You can either increase angle of attack to maintain lift, which will decrease speed further and you will stall; or you can pitch down aggressively to maintain speed, but it does not matter - sooner or later you will hit the ground.
If you have engines capable of producing enough thrust to overcome drag, you have created a wing with such a poor lift-to-drag ratio that it would be more efficient to simply point the engine down than to use wings.
That is assuming the wing does not break, of course.

Further extension will have the flaps act as air brakes as there is no flow attached to it (no flow over the airfoil)

No, Kevin, the aircraft will not stall. Maybe it cannot maintain level flight anymore, but it will fly just fine.

@PeterKämpf if an attempt is made to maintain level flight (assuming sufficient elevator authority), it will eventually stall due to ever decreasing airspeed (the engine is underpowered to overcome drag), am I correct?

@kevin: Yes, you are correct. But the flaps are meant for descent, approach and landing. Then the drag becomes quite helpful.

The airplane's reaction to full flap deflection depends strongly on how much of the wing chord is occupied by the flaps.  "The Full Ninety" (degrees) was once a popular marketing phrase, alluding to the racy title of a movie then in wide release, bragging about how the airplane's manufacturer had finagled the linkages for that much deflection to increase drag in particular for precise landings.  The chord fraction of such flaps was usually about one tenth.
I know of no production flaps with deflections beyond ninety degrees.

some planes like the DC 10 and 707 had a flap 50 configuration setting since it had 3 or 4 engine configurations, it could produce extra lift and it helped manage landing speed, though now since planes don't have 3 or 4 engine configurations, they don't need flaps 50 configurations anymore. but some companies like airbus go for more of flaps 30 mainly because of the plane design. if you have more modern planes like the 777 a350 e.c.t the design is improved so the plane would not need flaps above 40. if it does the flaps would most likely cause drag and stall more easily. making it useless for modern airliners to have flaps 50 or more.

More flaps means, among other things, more camber and thus slower stall speed.  More flaps cannot "cause stall more easily" unless the pilot imagines that they are Wile E. Coyote magic.

well, a higher flap setting means more drag, meaning more power to fly the aircraft at a certain speed, meaning more fuel wasted which can also give the reason on why most planes have a 40-degree max flaps setting.


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Human-powered flight in vs. out of ground effect?
There is an impressive flight (figure-of-eight) with a human-powered aircraft shown here:

Given the long wings of the Aerocycle 3, can it be considered to fly in ground effect for the whole flight?
Nothing wrong with that - the Ecranoplans are fascinating creations - but how much more power will be needed to lift it out of the ground effect, should it be desired?
Also, this thing is just screaming to be fitted with an e-bike powertrain...

Ground effect plays a role when the aircraft is within one wingspan of the ground, so the aerocycle is getting the benefit of lowered induced drag. It looks to be flying about a quarter of a span above the ground, so using the graph that is about two thirds of normal induced drag. Flying out of ground effect would therefore require about 50% more power.

But, am I wrong in thinking the primary reason for this reduction is due to the disruption of wingtip vortexes? If so, wouldn't the very narrow tip chord of this design already had much of this effect?

@MauryMarkowitz Wing tipped vertices aren't the cause of drag, they are simply a by product of lift. Drag is caused by the energy lost from pushing air downwards in order to keep the aircraft in flight. In ground effect the air pushed down quickly hits the ground and is deflected back up. Causing the airplane to generate more lift while having to move less air down. Thus less drag

@MauryMarkowitz The reduction in induced drag is disruption of the bound vortex, which is comprised of vortices along the whole span of the wing including the tips. The shape of the wingtip has only a minor effect on the tip vortex, which also persists in ground effect.


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What is this early biplane?
This is a 1910-1920 biplane that landed at Oregon Agricultural College. now Oregon State University. I've cropped out some of the people and horses. Thank you[]

What’s the source of the picture?

It seems like it's a picture taken of an image.
Would it be possible to get a higher-resolution picture?
That might help in identifying characterizing features

This is original I found on internet in 2018. I don't remember where. https://www.97330.com/biplane_CorvallisFirstAirplane_2.jpg

I put the original photo into the question instead of the edited version.

I think this is it. Similarities are: two bay strut braced biplane with upper single wing one extra bay wider than lower wing, inner struts just outside fuselage, overwing brace above outermost strut, visible structure under upper wing, same prop shape, very short rudder and skid landing gear with double wheels.
Your photo seems to have a different landing gear, a single center set with a second set of wheels at the back of the skids, which looks here like they just drag on the ground. This also appeared on floats.

Fowler-Gage NASM restoration with OX-5 (NASM)

1912 = 1pOB; 60-80hp Hall-Scott A-2/-3; span: (upper) 41'0" to 42'8" (lower) 30'0" v: 60. POP: 4 or 5 for exhibition pilots Robert Fowler (aka Fowler-Gage with 80hp Hall-Scott A-3, occasionally on floats), Roy Francis, Phil Parmalee, and J Clifford Turpin. Design carried forward to the twin-prop Patterson-Francis. The Fowler-Gage was donated to Smithsonian in 1950 and restored for display by NASM in 1988.

Here is another pic showing the single central float.

While the wings are similar, the original photo (I suggest using the link in the comments) has a prominent bracing from the engine to the central wheel / skid. Further, the Fowler Gage has triplane winglets, which I think would be visible on the photo despite its poor quality; and has a distinctive engine cylinder arrangement which doesn't appear to match on the photo either. Finally, there was a fuel tank mounted on top of the wing, which also isn't present. On balance I don't think it's a Fowler Gage.

@PartyArk It may not be the exact year, but I think you are wrong on the engine. Both aircraft have shiny V cylinders which can be seen in both photos. Landing gears are interchangeable and do not change the model of aircraft. A C180 on floats is still a C180. A single gear didn't work well and eventually got eliminated but if a C180 had a single skid gear, it would still be a C180.

I take your point, but the nature of the prominent chin on the Fowler Gage, and the way it lifts the engine / cylinders close to the top wing, and hence puts the prop above the line of the top of the fuselage just aren't replicated in the aircraft in the picture. In all I'd say different engine, missing winglets, missing fuel tank and unique undercarriage all point to a different a/c.


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What is this thin stream coming out from somewhere near the engine?
A friend of mine have recently had a flight from Rome to NYC, on a B-787 (Norse Atlantic), and he noticed this thin stream coming out from somewhere in the engine area, seen in this video. From his seat he could not see where exactly it's coming from. It started when the engine started, and continued throughout the entire flight.

My first thought was that it's something to do with the air-conditioning or pressurization system, but since i couldn't identify the exact location the steam is coming from, i can't say for sure.
Any idea?

Possibly related: https://aviation.stackexchange.com/q/100213/10025

It is oil from the combined drain mast and breather outlet. Norse uses RR trent 1000. The drain is for any water that gets into the cowling but empties on the ground and the breather is for the air/oil separator for oil that gets past various seals in the engine. Exhaust is normally only visible on the ground. At speed the air pressure increases and seals work properly. If visible in the air there was likely a damaged oil seal.

Here is a cutaway of the similar trent 500 showing part 52 (click to view full-size image):

No chemtrail then, what a pity

@sophit Oil is a chemical. Come to think of it, water is a molecule and also thus a chemical.

@slebetman: everything is actually chemical  But you know that I meant this.

The default behavior is for the image  tag to point to the uploaded image, but you can change that (as I did) so that it points to the original. Or indeed to any other URL.

I had the feeling that mentioning the airline will be important for the answer, I just didn't know how... thank you @Pilothead!

@sophit Literally a "chemtrail" for once


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How is fuel weight calculated?
I was having a conversation concerning airplanes and the calculated fuel. We were having a conversation about the Airbus A380. Based on this site:
http://www.modernairliners.com/airbus-a380/airbus-a380-specs/
It shows a capacity of 320,000 Litres. After some conversion (I am in the US)
320,000 Litres = 84,535 gallons
84,535 gallons = 710,000 lbs
Now that is based on water density. I've heard that jet fuel isn't exactly comparable to water? Is this true? I am trying to confirm because 700 thousand pounds of fuel sounds like a lot? Is there something I am missing? An average Olympic sized swimming pool carries about 660,430 gallons of water. How does this plane carry that much weight? And what would be the easiest way to explain this to a layman like myself?

How does it carry that much weight? By creating even more lift, because the structure and the payload weigh a considerable amount as well.

Just a minor thing, but I would recommend to avoid using decimals that are „introduced“ by converting units. The tank capacity won’t be exactly that many litres (and if it is, it’s still not very relevant), so converting it to 84,535 gallons is perfectly fine and, both from a „perceived precision“ and a readability standpoint, in my mind, preferable. Hope you don’t mind my comment on a minor detail!

Adding to @CptReynolds' comment, you typically want to consider the number of significant digits. The number of significant digits in 320,000 can be anywhere between two and six, but never more than six, so any final result should never have more than six significant digits, and quite possibly no more than two. With rounding, this makes your final weight figure 710,000 lbs (because 705 rounds up to 710). The number of significant digits is easier to see in scientific notation; for example, if the capacity was given as 3.20 * 10^5 L, we'd have known immediately to use three significant digits.

@CptReynolds and michael-kjörling - Thanks guys for the advice, I updated the original question to do some rough rounding up.

Why use water density? Can't you just look up for the fuel's density?

I just was doing a straight calculation and only recently was told that the water and fuel density were not the same. This was an assumption on my part since I know nearly zero about planes aside from the fact that they can take off and land.

It's the calculation and conversions I'm trying to wrap my head around. Because 85,000lbs of a liquid would seem to take up a lot of space and my friend and I were trying to figure out where all this liquid goes.

Fuel doesn't have the same density as water. We're not planning a real flight, so a quick and dirty fuel density figure from Wikipedia tells us:

In performance calculations, airliner manufacturers use a density of jet fuel around 6.7 lb/USgal or 0.8 kg/l.

So if we take your figure of 320,000 litres (it's a bit unclear quite how much of that is actually usable for flight, but that's a subject for another question), that's about 560,000lbs of fuel or around 254,000kgs.
Which, indeed, is a lot. The fuel is spread throughout the wings (and the trim tank in the tail), which are designed to carry the weight. If you look at What is the weight budget of a fully loaded A380?, you'll see how the fuel capacity interacts with the other weight specifications for the aircraft:

The maximum fuel weight is the difference between maximum ramp weight and zero fuel weight (which is 562,000−361,000=201,000kg)

Max take-off weight is a bit less than maximum ramp weight, but we'll handwave over taxi fuel for simplicity. The point here is that if you can fill the aircraft with cargo, it would be too heavy if you also filled it with fuel. If you want to take a full load of fuel, you'd have to reduce your payload to keep the total weight low enough. Working out the weight/fuel/range trade-offs for a given flight is what dispatchers and load planners do, using specialized software.

Others have already addressed the issue of calculating fuel weight, but I'd like to take a moment to discuss what you wrote in a comment to the question.

85,000lbs of a liquid would seem to take up a lot of space and my friend and I were trying to figure out where all this liquid goes.

One of the beauties of the metric system is that one liter is exactly equal to one cubic decimeter (the latter, of course, being a cube of 10x10x10 cm; in US terms, that's a shade under 4x4x4 inches). A liter, like a cubic decimeter, is a unit of volume, rather than a unit of mass.
320,000 liters thus corresponds directly to 320,000 dm3. In a more usable unit, this is 320 m3 because 1 m3 = 1,000 dm3.
Looking at Wikipedia, the wing area of the A380 is given as 845 m2.
If the entire wing area can be used for fuel tanks, which is not the case, and there are only fuel tanks in the wings, which is not the case, this means that the average height of the fuel tanks in the wings would need to be equal to 320 m3 divided by 845 m2, or about 0.38 meters; a little thicker than the long side of a piece of A4 or Letter paper. I haven't flown in an A380 recently, but I suspect that the wings are thicker than this. The fuel also isn't kept only in the wings; while I don't know about the A380's configuration specifically, it's common for large aircraft to have both wing tanks, a center tank within the fuselage, and a trim tank farther back in the fuselage.
Bottom line here, there's plenty of room for that amount of fuel.

Fuel comes out of the bowser and is metered in Litres (at least where I come from!). An aircraft is more interested in how much that is in kgs. So the person in charge of the fuelling has to take into account the SG or specific gravity of the fuel on that day. This varies according to the temperature. In the tropics it is usually around 0.780.
This means if the fuel has a SG of .780 it weighs 0.780 of 1 litre of of water @ 4deg C (water is used as the reference unit). As 1 Litre of water is equal to 1 kg, 1 Litre of Jetfuel at SG 0.780 is equal to 780grammes.
So if the bowser has metered out 100,000Litres of Jetfuel at SG 0.780, it will add 78,000kgs to the weight of the aircraft.
One flight I did was at maximum range of the B747-400. The flight-planning was done in HKG and they needed to know the actual SG as this will give the actual maximum weight of the fual they could carry. If I'm remember correctly the 747-400 can carry something like 170,000kgs of fuel but if the density is low you might not be able to fill it max weight-wise. I believe we uplifted around 167,000kgs that day.
There is another formula for gallons to Lbs but I cant remember it as I've worked mostly with Metric.

the formula for gallon in Lbs seems to be a simple conversion formula

The multiplicative conversion factors that Boeing uses for English to Metric are 0.45359237 for  pounds to kilograms and 3.78541180 for U.S. gallons to liters. Thus 2.20462262 for kilograms to pounds and 0.26417205 for liters to U.S. gallons. In the past it was common to use 2.2 to convert from kg to lb, but that was a poor practice because it could result in an aircraft departing when slightly over the max takeoff weight.

I asked for max fuel for the first three 747-400s in my weight & balance program, and it came up with a 163028 kg at 0.8028 kg/L (359415 lb at 6.7 lb/gal) for all three, so your memory of 167000 kg is reasonable. You might have had a higher density or larger tankage.


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Aircraft Carrier Launches: ABE Checks and Signals
Somehow I got hooked on videos of aircraft carrier flight deck operations, and have been binge-watching over the last couple of days. (Glad it's a long weekend...)
I've been able to understand many of the hand signals from the Aircraft Signals NATOPS Manual (NAVAIR 00-80T-113), but I'm missing a lot of the context of what I'm seeing, because much of the video footage focuses rather narrowly on specific individuals and tasks rather than showing the "bigger picture."
I actually have many more questions than I will put down in this first post, and I will likely post more later. But here I will start off with just a few questions about the "Aviation Boatswain's Mate - Equipment" (ABE) rating, because it looks the most interesting to me.
All questions reference this video, which has some pretty clear shots of ABEs at work. (Parenthetically, I assume that the reason there are two ABEs working the catapult attachment task is that the "hands-on" one is under instruction, and his work is being checked by the other one. Have I got that right?)

At 0:27 the two ABEs appear to be waiting for some kind of go-ahead signal from someone out of frame (to whom they are pointing?), before signaling for the aircraft to be brought forward to position the launch bar in front of the catapult shuttle. Who are they pointing at, and what condition needs to be satisfied before they can proceed?
At 0:38, before signaling for catapult tension, they go through what appear to be a series of visual check-ins with three (or maybe four) separate individuals out of frame:

ahead of the aircraft;
behind the aircraft on the near side;
ahead of the aircraft again (same individual as before?);
behind the aircraft on the far side.

These checks happen quickly enough that I believe they can only be looking
for simple thumbs-up signals. What are the roles of the specific individuals they are looking to, and what, specifically, are those individuals verifying that make it okay to proceed with catapult tensioning?

When tension is finally applied at 0:44, they make a final check of the holdback bar before getting clear. What possible failure modes of the holdback bar are they looking for, specifically?
At 1:01, when the catapult officer signals “launch,” the deckedge catapult operator (center of frame, with hands raised overhead to signal “final ready”) turns his whole body first left, then right, before actuating the catapult. Is he checking something (what?), signaling something (what?), or both?

These should really be broken up into different questions. And welcome!

I feel like they're related enough to be combined. If they're broken up, maybe the "what are they checking for" parts could be separated.

@Bageletas It's a tough call. I believe 1 & 2 belong together, because they are part of the same action sequence and both involve "checks and signals." 3 is also part of that sequence, but (per fooot) is only a check; and 4 is about a different crew member; so these two might be separable. My rationale for grouping all four, though, is that any respondent who really knows the ABE specialty will likely know the answers to all four. Making a potential respondent visit 3 different questions lessens the likelihood that they would answer them all, even if they theoretically could.

I thought this might be easy when I saw the title, but very detailed questions!  I was never an ABE, but I've taken a few hundred cat shots as pilot.  About the only one I can really answer is #4.  He is doing both - he is checking forward and aft to make sure all personnel and equipment is clear and the airplane is ready to shoot, and he is signaling to all on deck, (especially the boss in the tower) his clearing of the space by exaggerating his body movements rather that just turning his eyeballs and head.  Hope that helps a little!

I'll take a stab at this.  It's been many years, but I was a shooter (yellow vest, green helmet).  Someone with a better memory can chime in.
You're correct that one of the hook-up operators is under instruction (U/I).  There are also 2 shooters in this video; one of them is under instruction as well.  Sometimes the instructor will give a thumbs up to indicate that the U/I operator's signals are correct and should be obeyed.

Before 0:27 they are looking toward the "island" for a green beacon that indicates the Air Boss is ready for the crew to launch planes.  At 0:27 they see the beacon turn green, then they look to the shooter for the hook-up signal.  The shooter is checking for several things: green beacon on, deck clear forward, jet blast deflector (JBD) raised, nobody on the wrong side of the foul-deck line, proper aircraft configuration (flaps down, tailhook up, etc), wind speed hasn't dropped since the catapult steam setting was entered, and thumbs up from the squadron QA folks (white shirts, behind aircraft on both sides) who are watching the jet for proper functioning, no leaks, etc.  When all those conditions are met, the shooter gives the hook-up signal, which triggers the hook-up operator to call for the jet to taxi forward.  The yellow-shirt (ABH) receives the "rolling" signal from the hook-up operator, then signals the pilot to pull forward, which causes the tow bar to drop down in front of the shuttle.
I think they are checking for a thumbs-up from the center-deck operator (sitting in the hole next to the shooter; thumbs up indicates good catapult steam pressure and good wind over the deck, which the shooter is no longer monitoring).  They also may be looking at some of the same things the shooter is looking at.
The holdback bar needs to be properly set in its slot in the deck, properly attached to the aircraft, not leaking hydraulic fluid, and IIRC there's a shiny metal ring between the orange and white sections that indicates proper functioning and tension.
The deck edge turns his whole body so everyone can see that he's looking fore and aft for clear deck forward and JBD up, and maybe also so he can see past his arms which are raised so that everyone can see he's not pushing the launch button yet.  At this point the shooter hasn't been looking forward because he has been mainly focused on the pilot and aircraft while the engine is running up and the pilot goes through flight-control checks, salute, etc.

Additional comments: most of the time the shooter and center-deck operator are below decks inside the glass "bubble" but they do practice deck launches to stay proficient.  I did my shooting on an older ship that didn't have the bubble at all.  Needless to say, communication is purely visual because you can't hear anything.  Even the operators with radio or phone headsets can't hear anything when jet engines are blasting nearby.
Finally, if you think this looks complicated and dangerous, remember this video was taken in daytime in good weather.

Thanks for the answer and thanks for serving!

Great answer!  I can practically smell the jet exhaust again...

Love the additional details! And echoing @FreeMan, thank you for your answer and your service!